Myriads of sea-birds breed on the small islands along the coast or swarm about the bays, where the fish supply them with abundant food. The number of these birds, a matter formerly of only local interest, is now a subject of general importance, as to them are owing the deep guano beds which have converted the sterile Chincha Islands[5] into mines of wealth. The want of rain, which renders the greatest part of the Peruvian coast so utterly barren, is of the utmost advantage for the production of the guano; for if the Chincha Islands, like the Orkneys or the Hebrides, had been exposed to frequent storms, or washed by unceasing showers, they would have been mere naked rocks, instead of affording the richest deposits of manure the world can boast of. CHAPTER V. THE AMAZONS, THE GIANT RIVER OF THE TORRID ZONE. The Course of the Amazons and its Tributaries--The Strait of Obydos-- Tide Waves on the Amazons--The Black-water rivers--The Rio Negro-- The Bay of the Thousand Isles--The Pororocca--Rise of the River-- The Gapo--Magnificent Scenery--Different Character of the Forests beyond and within the verge of Inundation--General Character of the Banks--A Sail on the Amazons--A Night’s Encampment--The ‘Mother of the Waters’--The Piranga--Dangers of Navigating on the Amazons-- Terrific Storms--Rapids and Whirlpools--The Stream of the Future-- Travels of Orellana--Madame Godin. The Amazons, the giant stream of the tropical world, is of no less magnificent proportions than the Andes, where it takes its source. From the small Peruvian mountain-lake of Lauricocha, 12,500 feet above the sea, the Tunguragua, which is generally considered as the chief branch, rushes down the valleys. At Tomependa, in the province of Juan de Bracamoros, rafts first begin to burden its free waters; but, as if impatient of the yoke, it still throws many an obstacle in the navigator’s way; for twenty-seven rapids and cataracts follow each other as far as the Pongo de Manseriche, where, at the height of 1,164 feet above the level of the sea, it for ever bids adieu to the romance of mountain scenery. Its width, which at Tomependa exceeds that of the Thames at Westminster Bridge, narrows to 150 feet in the defile of the Pongo, which in some places is obscured by overhanging rocks and trees, and where huge masses of drift-wood, torn from the slopes by the mountain torrents, are crushed and disappear in the vertex.